Structures, such as valves and blowout preventers, which are designed to hold pressure under corrosive conditions preferably have an alloy steel exterior body for high strength and an interior lining of corrosion resistant metal. Such lining should be provided without weakening the alloy steel body, should completely cover the exposed interior and should be uniformly bonded to the body.
A stainless steel lining inserted into a valve passageway and flared at its ends is shown in U.S. Pat. No. 3,349,789. Another valve with an inserted liner is disclosed in U.S. Pat. No. 2,497,780. A lined article produced by the simultaneous extrusion of two metals in an impact die is disclosed in U.S. Pat. No. 3,648,351. Another process for extruding two metals in a single structure is disclosed in U.S. Pat. No. 2,088,223.
Prior to the present invention, lined pipe has been made by co-extruding a billet of two concentric tubes of different metals, e.g., carbon steel for the base metal and stainless steel for the lining. An extrusion process is acceptable for producing tubular elements but making structures, such as valve and blowout preventer bodies, requires complex shapes including flanges etc., rather than a straight extruded tube. Metal linings also have been deposited by welding, by electroplating and by explosion bonding.
Linings provided by bonding, such as by welding or explosive bonding, have a tendency to cause a change in the outer alloy steel body by the application of heat or explosive force so that the body may be weakened. Also, with all linings, sufficient lining material should be provided to assure a complete lining after machining.